Apparatus and method for a spray dryer

ABSTRACT

A spray dryer apparatus and method suitable for the production of detergents, cleaners and components thereof wherein the inner wall of the drying chamber is provided with an air-permeable textile material lining at a distance from the inner wall, and at least one outlet for compressed gas is provided between the inner wall and the textile material lining whereby adherence of sticky deposits on the inner wall of the drying chamber is avoided or reduced.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a spray dryer which is particularly suitablefor the production of detergents and/or cleaners and components thereofand which comprises a drying chamber, at least one spraying element forintroducing the material to be spray-dried into the chamber and meansfor introducing a heated gas into the chamber in co-current orcountercurrent to the descending spray-dried material.

2. Discussion of Related Art

Spray dryers of the type in question are known. They are used on anindustrial scale for the production of powder-form detergents orcleaners and components thereof known as “tower powders”. In these spraydryers, a coherent liquid mass or slurry is divided up by nozzles intosmall droplets which are then dried by a hot air stream flowing incountercurrent to the descending droplets, the liquid suddenlyevaporating.

Spray drying in the production of detergents/cleaners is characterizedon the one hand by the relatively high temperature of the drying gasused which can exceed 300° C. On the other hand, the material to bedried generally contains a large percentage of organic ingredients, moreparticularly surfactants, which are not only temperature-sensitive, theyalso tend to carbonize and self-ignite at the high temperaturesprevailing in the spray dryer if the product remains in the dryingchamber for longer than a few seconds.

Accordingly, in the production of detergents/cleaners and componentsthereof, it is important that the material to be spray-dried passthrough the spray dryer relatively quickly and, in particular, berapidly discharged from the dryer.

Unfortunately, some of the material to be spray-dried is inevitablydeposited onto the inner walls of the drying chamber where it graduallyheats up, dries out completely and, after a certain time, becomes sohard that it is extremely difficult to remove.

These deposits are formed in particular in the production ofdetergents/cleaners because the only partly dried-on particles, whichare rich in surfactants, have a very tacky surface. In addition, blackproduct particles are formed by carbonization and contaminate the towerpowder so that it no longer meets consumer quality requirements.

To solve the problems caused by hard deposits, carbonization and therisk of fire, operation of the spray dryer for the production ofdetergents/cleaners and components thereof is interrupted at regularintervals for the purpose of cleaning the inner walls of the chamber.

The problems mentioned above occur to a greater extent with moderndetergent formulations which contain particularly large amounts ofsurfactants. To prevent deposits formed on the inner walls of thespray-drying chamber from burning, not only is operation of the dryerregularly interrupted, the temperatures of the hot gas are also lowered.As a result, the performance of the spray dryer diminishes.

The deposits are formed all over the inner wall of the drying chamber,but especially in the lower region thereof which, generally, tapersconically downwards. The inclination of the inner walls in this coneleads to increased deposits which, moreover, become particularly hot inthis region because the hot drying gas enters the drying chamber in thevicinity of the tower cone.

Although the deposits could conceivably be removed by externally mountedknockers, the resulting deformation of the tower cone would result indamage to the surface and in unevenness in the inner wall which in turnwould result in increased deposits. Other disadvantages include thenoise generated, the uncontrolled cleaning and the difficulties involvedin removing particularly hard deposits.

Accordingly, the problem addressed by the present invention wassignificantly to ease the problems caused by deposits, carbonization andthe risk of fire in a spray dryer of the type mentioned at thebeginning. In addition, the operational interruptions for cleaning theinner walls of the drying chamber would only be necessary at very muchlonger time intervals.

DESCRIPTION OF THE INVENTION

According to the invention, the solution to this problem in a spraydryer of the type mentioned at the beginning is characterized in that atleast part of the inner wall of the drying chamber is lined with anair-permeable textile at a distance from the chamber wall and at leastone outlet for compressed gas, more particularly compressed air, isprovided between the chamber wall and the textile. In a preferredembodiment, the lower part of the inner wall and/or the inner wall inthe vicinity of the spraying elements and/or the inner wall below thisregion is/are lined with the textile.

The particles adhering to the inner walls of the spray dryer accordingto the invention are deposited onto the air-permeable textile which canbe cleaned simply and effectively from the back by exposure to a pulseof the compressed gas. When cleaned in this way, the textile expands andadhering particles fly off and are blown into the interior of the dryingchamber. There is no longer any need to interrupt the operation of thedryer to clean the walls.

Another advantage lies in the increased performance of the spray dryeraccording to the invention because the product contains feweragglomerates which, hitherto, would have been removed as oversizeparticles by sieving. The absence of deposits according to the inventionreduces the risk of fire and allows higher temperatures for the hot gasso that the performance of the spray dryer can be increased.

The gas used for cleaning may be compressed air. However, inert gases,for example nitrogen, combustion gases or the gas used for drying, forexample hot air or superheated steam, may also be used.

Since the problems mentioned at the beginning occur to a greater extentin a downwardly tapering drying chamber, the cone is lined with theair-permeable textile in a particularly preferred embodiment of theinvention.

The air-permeable textile lining according to the invention isadvantageous for all regions of the inner wall of the drying chamberwhere the product is preferentially deposited. Thus, in anotheradvantageous embodiment of the spray dryer according to the invention ofwhich the spraying elements are arranged in at least two horizontalplanes, the inner wall of the drying chamber is lined with the textilein the region between the planes and/or below the planes. In thisregion, the sprayed droplets still contain a relatively large amount ofliquid, particularly water, and accordingly have a particularlypronounced tendency to adhere to the inner wall of the drying chamber.

Woven fabrics combining high heat resistance with high tensile strengthare particularly suitable as the textile. The high tensile strengthenables the textile to be cleaned with relatively high gas pressures. Inone particular embodiment, the textile is a fabric of high-modulusfibers, more particularly polyamide and preferably aramide fibers.High-modulus fibers such as these are heat-resistant andnon-inflammable. They possess very high strength and glass anddecomposition temperatures of >400° C. and are therefore particularlysuitable for use in spray dryers which are used for the production ofdetergents/cleaners and components thereof and, accordingly, operatewith particularly hot drying gases. High-strength textiles of the typein question advantageously accommodate a relatively high pressure of thegas for cleaning the textile of up to 10 bar and, more particularly,from 3 to 8 bar.

The scope of the present invention encompasses various embodiments ofthe spray dryer which allow various modes of operation for the cleaningof the textile. Thus, the textile can be periodically freed fromadhering deposits by a pulse of compressed gas. However, continuouspulsation of the textile with the compressed gas is particularlyadvantageous. Accordingly, the invention proposes a control unit forvalves preceding the outlets by which the valves are intermittentlyopened and closed, the frequency and pulse duration in particular beingvariable.

In one particularly advantageous embodiment, the control unit isdesigned for a frequency of 1 to 10 per minute and for a duration of theopening pulse of 1 to 10 seconds.

In another preferred embodiment, the inner wall of the drying chamber isat least partly divided into segments and each segment is lined with atextile clamped to supports at its edges. The supports may be formed,for example, by narrow battens with rounded edges. With each pulse ofcompressed air, the textile is briefly inflated and widened towards theinterior of the drum. After the pulse of compressed air, theair-permeable textile gradually returns to its original position.

In another preferred embodiment of the invention, at least two outletsfor the gas are associated with each textile, being arranged in oppositeregions thereof, more particularly in the upper and lower regionsthereof. In this way, each textile can be alternately exposed to pulsesof the compressed gas from different directions so that the textile isalternately brought into one shape or the other and layers of driedproduct are prevented from forming locally on the textile. Even if notall parts of the textile are sufficiently moved by the individual pulseof compressed air to remove adhering product, substantially completecleaning of the textile can be achieved in this way.

In another embodiment of the invention, the throughput can beindividually adjusted through the outlets which are designed inparticular as nozzles for compressed air.

In one particularly advantageous embodiment of the invention, theoutlets are supplied with compressed gas by annular, substantiallyhorizontally extending gas distribution lines which are designed to beindividually actuated. This guarantees an adequate volume of gas eachtime the particular textile receives a pulse of compressed gas.

Although by far the largest amount of deposits and fine dust accumulateson the outside of the textiles and, according to the invention, is blowninto the interior of the drying chamber, fine dust can also collectbetween the textile and the inner wall of the chamber over a period oftime. To remove this fine dust during the pulses of compressed gas, ventvalves are provided on the outside of the drying chamber in the vicinityof the textile lining.

The present invention also relates to a method of operating a spraydryer of the type described above, preferably for the production of atacky product or a product with a tendency to agglomerate, moreparticularly detergents and/or cleaners or components thereof. The hotgas used for this purpose has an entry temperature of up to 300° C. Thetextile is preferably cleaned by compressed air under a pressure of 4 to7 bar excess pressure which acts periodically on the textile with afrequency of 1 to 10 per minute and a pulse duration of 1 to 10 seconds.

DESCRIPTION OF THE DRAWINGS

One example of embodiment of the spray dryer according to the inventionis described in detail in the following with reference to theaccompanying drawings, wherein:

FIG. 1 is a schematic perspective view of the conical part of a spraydryer.

FIG. 2 shows the supply lines for the compressed gas for cleaning thetextiles arranged in the conical part.

FIG. 3 shows the sequence of compressed gas pulses as a function oftime.

FIG. 4 shows a detail of the cone from inside.

FIG. 5 is a section on the line V—V of FIG. 4.

In the drawings, the same reference numerals have the same meanings and,accordingly, may only be explained once.

The lower part of a spray dryer shown in FIG. 1 has a cylindrical middlesection 1 which tapers conically downwards. A hot drying gas 20 isprovided to the spray dryer, above a cone 2 of the spray dryer, with aconventional hot drying gas supply 22. A material to be spray-dried 24is also provided to the spray dryer, above the cone 2, with conventionalspraying elements 26.

In this embodiment, only the cone 2 and not the middle section 1 islined with the air-permeable textile. The cone 2 is divided into threeannular, vertically adjacent layers 10, 10′, 10″ which, in turn, areperipherally divided into individual segments 3. In the interests ofclarity, only a few and not all of the segments are denoted by thereference numeral 3.

In addition, FIG. 1 shows the main supply line 4 for compressed airwhich supplies five ring lines 5 with compressed air. According to theinvention, the compressed air is used to clean the textiles (not shownin FIG. 1) arranged on the inner wall of the cone.

The delivery of the compressed gas in the conical region of the spraydryer is shown in detail in FIG. 2. The main supply line 4 is suppliedfrom a compressed air source (7 bar) via two shutoff valves 6. Thebranches from the main supply line 4 to the five ring lines are denotedby the letters A to E. Compressed air is introduced into these ringlines through a magnetic valve 7 operable by a control unit (not shown)and through a shutoff valve 8. Lines lead from each ring line—providedwith a pressure gauge 9—to the nozzles 14. For each segment, there is anozzle arranged in the upper region and a nozzle arranged in the lowerregion. In the interests of clarity, FIG. 2 shows only one nozzle—ratherthan the plurality of nozzles—for each ring line 5.

The control unit opens and closes the magnetic valves 7 in a certainpredetermined rhythm of which one example is shown in FIG. 3. In theboldly marked time intervals of this time scale, the particular magneticvalve 7 is opened; in the thinly drawn time intervals, it is closed. Itis essential that the two ring lines supplying the same textiles orsegments with compressed air are not opened simultaneously, butalternately. In this way, the textile undergoes a different change inshape with each pulse of compressed air so that even awkwardly situatedparts of the textile can be cleaned, i.e. freed from deposits.

The arrangements of the textile-lined segments and the compressed-airnozzles with their feed lines are shown in detail in FIGS. 4 and 5. Thesegments 3 of the three layers 10, 10′, 10″ are each lined with atextile 11 which consists of a woven aramide cloth or similar materialand which is horizontally and vertically clamped by narrow battens 12with rounded edges. Nozzles 14 arranged on the wall 13 of the coneinject pulses of compressed air into the space between the wall 13 ofthe cone and the textile 11 at predetermined time intervals.

The segments 3 in the two upper layers 10, 10′ are each provided with anozzle 14 arranged in the upper region and with a nozzle 14 arranged inthe lower region. The segments 3 of the lower layer 10″ have only one,substantially centrally arranged nozzle 14.

The supply of compressed air to each nozzle can be individually meteredor completely interrupted by a control and shutoff valve 15.

FIG. 5 additionally shows a closable vent opening 16 which enables finedust collecting between the textile 11 and the wall 13 to be blown outat regular intervals.

List of Reference Numerals

1 middle section

2 cone

3 segment

4 main supply line

5 ring line

6 shutoff valve

7 magnetic valve

8 shutoff valve

9 pressure gauge

10 layer

10′layer

10″ layer

11 textile

12 batten

13 wall

14 nozzle

15 control and shutoff valve

16 vent opening, vent valve

What is claimed is:
 1. A spray dryer for the production of detergents,cleaners, and components thereof, the spray dryer comprising: a dryingchamber, at least a part of an inner wall of the drying chamber beinglined with an air-permeable textile spaced from the inner wall, and atleast one outlet intermittently providing compressed gas between and theinner wall of the drying chamber and the textile; at least one sprayingelement for introducing material to be spray-dried into the dryingchamber; and means for introducing a heated gas into the drying chamberto the spray-dried material.
 2. A spray dryer as in claim 1, wherein thelower part of the inner wall of said drying chamber, is lined with saidtextile.
 3. A spray dryer as in claim 1 wherein said drying chambertapers conically downwards to form a cone section and the cone sectionis lined with said air-permeable textile.
 4. A spray dryer as in claim1, wherein an outlet for compressed gas is arranged in said dryingchamber in at least two horizontal planes and between the inner wall ofthe drying chamber and the textile, and the inner wall of the dryingchamber is lined with said textile in the region between the horizontalplanes.
 5. A spray dryer as in claim 1 wherein said textile is a wovenfabric of high-modulus fibers.
 6. A spray dryer as in claim 5 whereinsaid fibers are selected from polyamide and aramide fibers.
 7. A spraydryer as in claim 1 wherein the outlet for compressed gas provides a gasunder a pressure of up to 10 bar.
 8. A spray dryer as in claim 1 whereinthe outlet for compressed gas is equipped with valves and a control unitfor said valves to intermittently open and close said valves.
 9. A spraydryer as in claim 8 wherein said control unit intermittently opens saidvalves at a frequency of 1 to 10 times per minute and for a duration of1 to 10 seconds.
 10. A spray dryer as in claim 1, wherein the inner wallof said drying chamber is partly divided into segments, each segmentbeing lined with said textile.
 11. A spray dryer as in claim 10 whereinat least two outlets for said compressed gas are associated with eachsegment lined with said textile and are disposed in opposite regionsthereof.
 12. A spray dryer as in claim 11 wherein the throughput of saidcompressed gas can be individually adjusted through said outlets.
 13. Aspray dryer as in claim 12 wherein said outlets are supplied withcompressed gas from annular, substantially horizontally-extending gasdistribution lines, the gas distribution lines being individuallyactuated.
 14. A spray dryer as in claim 1 having vent valves on theoutside of said drying chamber in the region of the textile lining. 15.A method for preventing the accumulation of sticky deposits on an innerwall of a spray dryer used for the production of detergents, cleaners,and components thereof, the method comprising the steps of: lining atleast part of an inner wall of a drying chamber of said spray dryer withan air-permeable textile material at a distance from said inner wall;and providing at least one outlet for intermittently supplying acompressed gas between said inner wall and said textile.
 16. A method asin claim 15 wherein said textile material comprises a woven fabric ofhigh-modulus fibers.
 17. A method as in claim 15 wherein said textilematerial is selected from polyamide and aramide fibers.
 18. A method asin claim 15, further comprising the step of introducing a compressedgas, via the outlet for a compressed gas, into said drying chamberbetween the inner wall of said drying chamber and said textile materialwhereby sticky deposits formed on said textile material are releasedtherefrom.
 19. A method as in claim 18 wherein said compressed gas isintroduced under a pressure of up to 10 bar.
 20. A method as in claim18, further comprising the step of providing vent valves on the outsideof said drying chamber in the region of the textile lining.